Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $55.65   4.694%   $58.2622   $58.26   $58.25   $58.30  
  Purchase #2 $174.96   12.118%   $196.1617   $196.16   $196.15   $196.20  
  Purchase #3 $192.46   6.180%   $204.354   $204.35   $204.35   $204.40  
  Purchase #4 $79.76   8.683%   $86.6856   $86.69   $86.70   $86.70  
  Purchase #5 $159.69   13.764%   $181.6697   $181.67   $181.65   $181.70  
  Purchase #6 $193.84   12.157%   $217.4051   $217.41   $217.40   $217.40  
  Purchase #7 $47.82   5.800%   $50.5936   $50.59   $50.60   $50.60  
  7 purchase totals = $904.18       $995.1319   $995.13   $995.10   $995.30